1. Field of the Invention
The present invention relates to a method of obtaining a profile of a polishing member used in a polishing apparatus which polishes a surface of a workpiece, such as a wafer, and more particularly relates to a method of obtaining a sliding-distance distribution of a dresser on the polishing member by a simulation of a dressing operation.
The present invention further relates to a method of obtaining a sliding vector distribution of a dresser which can be used for an evaluation of a dressing operation of a polishing member.
Furthermore, the present invention relates to a polishing apparatus which can perform the above-mentioned methods.
2. Description of the Related Art
As a more highly integrated structure of a semiconductor device has recently been developed, interconnects of a circuit become finer and dimensions of the integrated device decrease. Thus, it becomes necessary to polish a wafer having films (e.g., metal film) on its surface to planarize the surface of the wafer. One example of the planarization technique is a polishing process performed by a chemical-mechanical polishing (CMP) apparatus. This chemical-mechanical polishing apparatus includes a polishing member (e.g., a polishing cloth or polishing pad) and a holder (e.g., a top ring, a polishing head, or a chuck) for holding a workpiece, such as a wafer, to be polished. The polishing apparatus of this type is operable to press a surface (to be polished) of the workpiece against a surface of the polishing member and cause relative movement between the polishing member and the workpiece while supplying a polishing liquid (e.g., an abrasive liquid, a chemical liquid, slurry, pure water) between the polishing member and the workpiece to thereby polish the surface of the workpiece to a flat finish. Such a polishing process performed by the chemical-mechanical polishing apparatus yields a good polishing result due to a chemical polishing action and a mechanical polishing action.
Foam resin or nonwoven cloth is typically used as a material of the polishing member used in such chemical-mechanical polishing apparatus. Fine irregularities (or asperity) are formed on the surface of the polishing member and these fine irregularities serve as chip pockets that can effectively prevent clogging and can reduce polishing resistance. However, continuous polishing operations for the workpieces with use of the polishing member can crush the fine irregularities on the surface of the polishing member, thus causing a lowered polishing rate. Thus, a dresser, having a number of abrasive grains, such as diamond particles, electrodeposited thereon, is used to dress (condition) the surface of the polishing member to regenerate fine irregularities on the surface of the polishing member.
Examples of the method of dressing the polishing member include a method using a dresser (a large-diameter dresser) that is equal to or larger than a polishing area used in polishing of the workpiece with the polishing member and a method using a dresser (a small-diameter dresser) that is smaller than the polishing area used in polishing of the workpiece with the polishing member. In the method of using the large-diameter dresser, a dressing operation is performed, for example, by pressing a dressing surface, on which the abrasive grains are electrodeposited, against the rotating polishing member, while rotating the dresser in a fixed position. In the method of using the small-diameter dresser, a dressing operation is performed, for example, by pressing a dressing surface against the rotating polishing member, while moving the rotating dresser (e.g., reciprocation or oscillation in an arc or linearly). In both methods in which the polishing member is rotated during dressing, the polishing area on the surface of the polishing member for use in the actual polishing is an annular region centered on a rotational axis of the polishing member.
During dressing of the polishing member, the surface of the polishing member is scraped away in a slight amount. Therefore, if dressing is not performed appropriately, unwanted undulation is formed on the surface of the polishing member, causing a variation in a polishing rate within the polished surface of the workpiece. Such a variation in the polishing rate can be a possible cause of polishing failure. Therefore, it is necessary to perform dressing of the polishing member in a manner as not to generate the undesired undulation on the surface of the polishing member. One approach to avoid the variation in the polishing rate is to perform the dressing operation under appropriate dressing conditions including an appropriate rotational speed of the polishing member, an appropriate rotational speed of the dresser, an appropriate dressing load, and an appropriate moving speed of the dresser (in the case of using the small-diameter dresser).
The dressing conditions are adjusted based on a profile (i.e., a cross-sectional shape of the polishing surface) of the polishing member that has been dressed. In order to obtain the profile of the polishing member, it is necessary to actually perform the dressing operation of the polishing member and measure thicknesses of the polishing member (or surface heights of the polishing member) at plural measuring points with use of a thickness measuring device, such as a micrometer. However, obtaining the profile of the polishing member by way of the actual measurement is a time-consuming operation and increases costs.
Indexes for evaluating the dressing of the polishing member may include the profile and a cutting rate of the polishing member. The profile of the polishing member represents a cross-sectional shape along the radial direction of the polishing surface of the polishing member. The cutting rate of the polishing member represents an amount (or a thickness) of the polishing member that has been scraped away per unit time by the dresser. The profile and the cutting rate can be estimated by a sliding-distance distribution along the radial direction of the polishing member.